Importing mp4s rarely works

[English Services]

I'm using LR 10.3 and have been a LR user for 12+ years. The past two weeks video files have not shown up in LR. The files are in the folder (in Windows Explorer) but aren't registered in LR. It is as if LR can't handle large files. The import session takes hours and when I get tired and "x" out, even some RAW files fail to import. This is a recent problem. Might it have something to do with this new version?

[GoldingD]

How large  are  thee  files. LrC does have limits.

[English Services]

Sometimes they are 500MB, sometimes larger. My LR catalog is 10.65 GB and I have 32GB of RAM. I don't know why my system can't handle the pictures and videos. 

[GoldingD]

even some RAW files fail to import

When you are importing those MP4 files and RAW files?

Or just importing RAW files?

If both, do the RAW files import just fine when you attempt to import just them?

[English Services]

Yes, the RAW files usually do fine. Today  I shot a wedding and first saved everything on the HDD and then imported them from their place on the hard drive. That worked without a hitch. However, the 29-minute long videos divided into two files (17:13 and 12:37; 2GB and 1.5GB respectively)...interesting.